Vaccinated people can be infected by and transmit the coronavirus Alpha variant

Outbreaks at two care homes in São Paulo state (Brazil) show that even people who have been vaccinated with one dose of the AstraZeneca vaccine or two doses of CoronaVac can transmit the virus. The cases were asymptomatic or mild and did not require hospitalization, but underscore the importance of rapidly vaccinating the entire population while continuing to require face coverings and social distancing even for those who have been vaccinated.

By André Julião  |  Agência FAPESP – Two outbreaks of SARS-CoV-2 caused by transmission of the Alpha variant show that even people who have been vaccinated can spread the virus and fall sick with COVID-19, but also that vaccination protects them from developing the severe form of the disease. The findings are based on genetic sequencing of the strains that infected residents and staff at two care homes in Campinas, São Paulo state, Brazil. The average age of the infected residents was above 70. They had taken one dose of the AstraZeneca vaccine or both doses of CoronaVac. The only patient who died was an 84-year-old with Alzheimer’s.

The study was supported by FAPESP and posted on Preprints with The Lancet (not yet peer-reviewed). 

“The results show that people who have been vaccinated can be infected by the Alpha variant and, whether or not they contract the disease, can transmit the virus to people who haven’t been vaccinated. This is a concern because it could create a selection bottleneck for strains that may cause fresh outbreaks of the disease even in those who have been vaccinated. It also shows the importance of maintaining social distancing measures and enforcing mask wearing,” said José Luiz Proença Módena, principal investigator for the study. Módena is a professor at the University of Campinas’s Biology Institute (IB-UNICAMP). 

A previous study by the group showed that blood serum from patients given CoronaVac created fewer antibodies against the Gamma variant (P.1) than against the original viral strain, suggesting that people could be infected even after they had been vaccinated (more at: agencia.fapesp.br/35415/). 

In an article published in April, researchers at the University of Oxford show that the alpha variant can infect people who have been immunized with the Pfizer vaccine or the AstraZeneca vaccine.

“Our article is one of the first reports of transmission dynamics in a SARS-CoV-2 variant of concern in vaccinated people,” Módena said. “At the same time, the severity rate is very low, much lower than we’d expect in a population with such a high average age, so it shows the protective effect of vaccination against the development of COVID-19.”

The study points to sustained viral transmission in outbreaks that were contained thanks to rapid diagnosis by the City of Campinas Department of Health Surveillance and immediate isolation of those infected. As a result, only about half the groups involved were infected.

The researchers measured viral loads in the vaccinated people who had been infected at both locations, but found no statistically significant differences between the two vaccines. They also measured the quantity of neutralizing antibodies against the Alpha variant in those who tested positive.

“We found no correlation between the severity of the disease and the titer [quantity] of neutralizing antibodies,” Módena said. “Subjects with symptoms had more antibodies than those without, probably in response to infection and not to the vaccine. That means protection doesn’t necessarily depend on antibodies alone but also on other components of the immune response induced by vaccination.”

Mild cases and asymptomatic cases

The Alpha variant, previously known as B.1.1.7, was first detected in September 2020 in the United Kingdom, and was behind the second wave of the pandemic there and in other European countries. In Brazil it was first reported in December 2020, and its presence has been confirmed in more than ten states.

In the latest study the researchers sequenced viral genomes from residents and staff of two care homes in Campinas. The sequencing was supported by the Brazil-UK Center for Arbovirus Discovery, Diagnosis, Genomics and Epidemiology (CADDE), which is funded by FAPESP. 

In one of the outbreaks, at a home for retired nuns, 15 of the 18 residents and seven of the eight staff had been given one dose of ChAdOx1, the vaccine developed by pharmaceutical company AstraZeneca in partnership with the University of Oxford. Their average age was 73. Sixteen cases were confirmed, half mild and half asymptomatic. There were no moderate or severe cases, and none required hospitalization.

At the other location, a retirement home for men and women, 32 out of 36 residents and ten of the 16 staff were given two doses of CoronaVac, the vaccine produced by Chinese company SinoVac in partnership with Butantan Institute, a research institution in São Paulo. Eighteen of the 22 cases (75%) were asymptomatic, and the other four were mild. The average age in this instance was 77.

At the same home, an 84-year-old resident with Alzheimer’s manifested symptoms of COVID-19 (later confirmed) 21 days after taking the second dose of the vaccine. He died after a hospital stay of some 20 days.

As the authors note, the results show that the vaccines confer protection against severe COVID-19, adding that as large a proportion of the population as possible must be vaccinated fast. Another message is that vaccinated people should continue to comply with non-pharmacological requirements such as mask wearing and social distancing.

The article “Clusters of SARS-CoV-2 lineage B.1.1.7 infection after vaccination with adenovirus-vectored and inactivated vaccines: a cohort study” is at: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3883263.