The hepatitis B vaccine seems to reduce the risk of developing diabetes, and not just by preventing the infection.

The vaccine is routinely offered to infants in most countries, usually via three doses. In the US, this became part of the vaccination programme in 1991, so only .

Scientists have previously found . This may be due to the hepatitis B virus – which infects the liver and spreads through blood, semen and vaginal fluids – from the blood. This could raise the risk of diabetes, where blood sugar levels are persistently too high.

But prior studies have not looked at whether the vaccine might reduce diabetes risk among a group of both immunised and non-immunised people who haven’t contracted hepatitis B, which would suggest the effect acts independently of just preventing the infection.

To explore this, at Taipei Medical University in Taiwan and her colleagues analysed the health records of more than 580,000 people living across the US, Europe, Africa, Latin America, the Middle East and the Asia-Pacific. On average, these records spanned nearly four years for each individual between 2005 and 2023.

None of the participants, who were aged between 18 and 90, had any kind of diabetes or had been infected with the hepatitis B virus, according to their records and the absence of infection-specific blood markers. About half of them had received a hepatitis B vaccine, gauged according to levels of virus-specific antibodies in their blood.

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The team found the vaccinated participants had an overall 15 per cent lower rate of diabetes – defined as them either receiving a diagnosis, having a persistently high blood sugar level or being prescribed diabetes drugs – than their unvaccinated counterparts. The vast majority of cases were type 2 diabetes, the most common form of the condition. The results will be presented at the European Association for the Study of Diabetes Annual Meeting in Vienna, Austria.

Although this is observational research, the scientists also found a dose-response effect, where the vaccinated participants with higher levels of hepatitis B-specific antibodies were less likely to develop diabetes than those with lower levels. Differences in antibody levels may be a reflection of how many vaccine doses the individual participants received, how recently they were immunised or general variation in immune responses.

As to the mechanism, the fact none of the participants had knowingly been infected with hepatitis suggests being immunised reduces diabetes risk independent of just preventing infection, says Phan. One potential explanation is it somehow reduces chronic inflammation that damages the liver and pancreas, which release hormones that regulate blood sugar levels, like insulin, she says.

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However, the scientists can’t rule out the possibility that part of the vaccine’s protective effect comes from preventing the infection, she says. They hope to explore the potential pathways involved, and how they may vary between different forms of diabetes, in studies in mice, says Phan.

It is possible people who get vaccinated are simply more likely to make lifestyle choices that reduce type 2 diabetes risk, such as eating a healthy diet and exercising regularly. “People who are prone to get vaccinated are generally people who are more conscious about living a healthy life,” says at the University of Veterinary Medicine Hannover in Germany.

The team accounted for factors that could affect the results, such as the participants’ age, sex and whether they smoked or had other conditions, like obesity and high blood pressure. But Osterhaus maintains the influence of such factors cannot be ruled out.

The most commonly used covid-19 vaccines are safe in pregnancy, a study has confirmed.

There has been a lack of clarity over the risks of covid-19 and vaccines against it during pregnancy throughout much of the pandemic. In the UK, covid-19 vaccines began being rolled out in December 2020, but were not offered to pregnant people until April 2021.

Worldwide, pregnant people are now broadly encouraged to get vaccinated against the coronavirus. But in the UK, .

To better understand the vaccines’ safety profile, at the British Columbia Children’s Hospital Research Institute in Canada and his colleagues surveyed 191,360 people, aged 15 to 49, between December 2020 and November 2021. Over these 11 months, the alpha, beta, gamma and delta coronavirus variants were .

The participants, who were from seven Canadian provinces, self-reported any health issues they may have experienced in the seven days after they received the first or second dose of a Pfizer/BioNTech or Moderna coronavirus vaccine. The team didn’t include people who received modified adenovirus vaccines, such as the Oxford/AstraZeneca vaccine, as only a relatively small number of pregnant people in Canada were immunised with this vaccine type.

The participants, of whom more than 97 per cent identified as women, were split into three groups: pregnant people who were vaccinated against covid-19, unvaccinated pregnant people and people who were vaccinated but not pregnant.

“This study was looking at whether there were any complications associated with [the coronavirus] vaccine doses during pregnancy,” says at the University of Toronto in Canada, a co-author of the study. The study didn’t ask whether the vaccine protects pregnant people from severe covid-19, which is supported by other research, she says.

The researchers found that in the seven days after a first vaccine dose, 1.5 per cent of the 5597 vaccinated pregnant people reported a stillbirth or miscarriage, which resulted in hospitalisation in some cases. This is compared with 2.1 per cent of the 339 unvaccinated pregnant people who experienced a stillbirth or miscarriage in the seven days before they were surveyed.

For comparison, the researchers assessed the hospitalisation rate of the non-pregnant but vaccinated participants. Of these, just 0.6 per cent were admitted for any reason in the seven days after their first vaccine dose.

“The one thing that all women who are pregnant worry about is the baby,” says McGeer. “In this sizable study, we were unable to detect any adverse events associated with pregnancy for those who got the vaccine.”

Other serious pregnancy complications – such as vaginal bleeding, abnormal foetal heart rate and reduced foetal movement – were rarely reported by any of the participants. Although the rate of these events was low, it was comparable between the pregnant participants, regardless of whether they had been vaccinated against covid-19.

“It is very reassuring that there is no evidence of any safety concerns associated with vaccination in pregnancy, especially as high levels of vaccination hesitancy in pregnancy persist,” says at the University of Edinburgh in the UK.

The team also found that just 4 per cent of pregnant people reported less serious health issues, such as muscle pain and headaches, in the seven days following their first vaccine dose, rising to 7.5 per cent in the week after a second dose.

Meanwhile, 6.3 per cent of the vaccinated non-pregnant people reported mild side effects in the week after dose one, increasing to 11.3 per cent in the seven days after dose two.

It is unclear why pregnant people experienced fewer mild symptoms after vaccination than non-pregnant people, says McGeer. It might be due to the way the immune system changes when someone is pregnant, she says.

The , the UK’s and the  in the US all recommend that pregnant people get vaccinated against the coronavirus.

Past research has shown the potential risks of catching covid-19 in pregnancy. According to a study published in July, having covid-19 in late pregnancy is linked to a seven-fold higher risk of premature birth.

A more recent study review found that pregnant people with covid-19 are more likely to experience heart complications than those who aren’t pregnant.