Why have so many contracted Covid-19 twice, or in some cases three times, during the pandemic?
In recent months, a second bout of Covid-19 has been reported by more people who tested positive last year, although there are no official statistics on reinfections here.
With the arrival of the Omicron variant in December, this has become more evident and reinfections appear to be more frequent in the wave that started with the BA.1 version, followed by the now dominant BA.2 version.
After being infected with Covid-19, the body produces a kind of protective immune response.
It mobilizes antibodies that, together with T cells, are said to provide protection for about six months.
However, in addition to being highly infectious, Omicron is better at evading immune responses to the Delta or Alpha variants.
People who thought they were safe six months or more after contracting it have been hit by the virus again.
Vaccines and Reinfection
We now know that Covid vaccines are best for preventing serious diseases. But their ability to protect us from infection is lower and declining.
Professor Kingston Mills, from Trinity College’s School of Biochemistry, said three doses of vaccine protect against severe Covid-19 disease but “do not actually prevent infection”. Vaccination followed by infection gives very good immunity, he said.
The BA.2 form of Covid-19 has strayed so far from the original form of the coronavirus that vaccine-induced antibodies against it are very weak, he added.
“When you get an infection, you generate antibodies against the same virus that you are exposed to again. There is a higher level of immunity generated by the vaccines followed by infection,” he said.
The combination of vaccination and infection enables the body to fight off the virus better.
More than 700,000 people are eligible for a booster shot, and some of them are waiting three months for the vaccine after contracting Covid-19.
Prof Mills said the duration of immunity from infection is shorter than infection after receiving a vaccine. It falls off earlier after the jab. The HSE is still asking people who have contracted Covid-19 to come back for the booster after three months.
Get Omicron twice
The chances of getting the BA.1 and then the BA.2 are considered slim. However reports have quoted some instances where this has happened.
They have been observed mainly in younger people and in unvaccinated people.
Second refresher shot
Prof Mills said he believes the most effective second booster shot for the majority of the population would be some type of vaccine developed specifically for Omicron.
Updated vaccines were due in March or April but were delayed to cope with current variants.
However, he said a booster shot from existing vaccines could be given to high-risk groups such as the immunocompromised.
The National Immunization Advisory Committee (NIAC) is expected to decide shortly who should receive a second booster shot and when. Booster shots will help make it harder for BA.2 to cause serious illnesses, whether they affect people once or twice.
There is no guarantee that a second dose of Covid-19 will be any easier. People reinfected during last winter’s alpha wave were less sick.
After Delta arrived in mid-2021, those reinfected found they were sicker.
Omicron is less serious, but there are many people who are unwell, although few require hospitalization. The severity of reinfection is affected by factors such as the variant, the strength of the immune system, and whether someone is vaccinated and boosted.
https://www.independent.ie/irish-news/health/why-growing-numbers-of-people-in-ireland-are-being-hit-with-more-than-one-covid-19-infection-during-pandemic-41512798.html Why more and more people in Ireland are affected by more than one Covid-19 infection during a pandemic