Immunisation Weekly Update:

1. Flu and COVID can trigger heart attacks and strokes
2. Diphtheria outbreak in NT
3. Japanese encephalitis – Stay safe from mosquitoes during school holidays
4. Pre-travel measles vaccination
5. Education

Flu and COVID can trigger heart attacks and strokes

Research has found that respiratory virus infections such as influenza and COVID can act as a trigger for heart attacks and strokes.

Following influenza infection, a patient’s risk of a heart attack increases by almost 5.4 times, and their risk of stroke by 4.7 times. The risk period is relatively short, from a few days up to weeks, and tapers off following infection. COVID can also act as a trigger, although there is not enough data to accurately quantify the proportion of risk increase.

People who are particularly vulnerable to this are those who also have existing traditional risk factors, such as high cholesterol or blood pressure, diabetes, or smokers.

The influenza vaccine is as effective as common heart medications at preventing heart attacks and strokes

Research has consistently shown that annual influenza vaccination reduces major cardiovascular risk by one-third, especially in those who have moderate-to-high risk. This is similar to the effect of many cholesterol-lowering medications.

Several recent studies indicate that the influenza vaccine appears to prevent cardiovascular events in three ways:

• By preventing influenza
• By stabilising vulnerable plaques inside blood vessels by altering the response to inflammation
• By preventing other viral illnesses via trained immunity

Heart attacks and strokes are among Australia’s biggest killers; recommending the influenza and COVID vaccines to your patients can bring significant benefit to our public health.

The influenza vaccine is recommended annually for everyone six months and over

In 2025, NSW recorded its highest number of influenza cases on record, with a 15.8% jump from 2024. The high-risk groups of children aged under 5 and adults aged 65+ only had vaccination coverage of 25.4% and 59.5% respectively.

Free influenza vaccines are available for these groups and other eligible people under the National Immunisation Program.

Diphtheria outbreak in NT

Travellers planning to visit the Northern Territory during the holiday period are advised to ensure their diphtheria vaccinations are up to date, following a confirmed outbreak in Darwin and Alice Springs.

As of 31 March 2026, NT Health has reported four cases of respiratory diphtheria and an ongoing number of cutaneous diphtheria cases. Diphtheria is a vaccine‑preventable disease that can cause serious illness, particularly in under‑vaccinated individuals.

• Children, adolescents, and adults should be up to date with recommended diphtheria‑containing vaccines (DTPa or dTpa).
• dTpa vaccination during pregnancy is essential to protect newborns; a single dose is recommended in each pregnancy and is funded under the National Immunisation Program.
• Healthcare workers should confirm their vaccination status and ensure they have received a diphtheria‑containing vaccine within the past 10 years.

Returning travellers to affected regions and close contacts of confirmed or suspected diphtheria cases should be clinically assessed and tested where indicated, regardless of vaccination status.

Contacts should be actively monitored for symptoms of respiratory or cutaneous diphtheria during the incubation period.

Suspected cases and identified close contacts must be promptly notified to the Public Health Unit (PHU) to enable timely public health management, including contact tracing, prophylaxis, and exclusion advice.

Japanese encephalitis – Stay safe from mosquitoes during school holidays

NSW Health is reminding people to protect themselves from mosquito bites ahead of the upcoming school holidays, as continuing warm weather and wet conditions mean mosquitoes are still around in significant numbers, particularly in the greater Sydney region.

People planning to travel to high-risk regions in the school holidays should have a discussion with their vaccination provider as soon as possible.

NSW Health recently expanded free access to the Japanese encephalitis (JE) vaccine to people who plan to visit high-risk local government areas​ for outdoor recreational activities including camping, caravanning, boating, hunting and fishing while mosquito activity remains high.

The JE vaccine is also free for anyone who lives or routinely works in various inland regions as well as people who work in some high-risk occupations.

Pre-travel measles vaccination

A new report confirms that almost all cases of measles in Australia are either acquired overseas or related to an overseas acquired case – especially around school holidays.

Measles was most common among people who:  

• were aged 20 to 49 years – who accounted for 57% of total notifications 
• either were unvaccinated (47%), had an unknown vaccination status (30%), or were under-vaccinated (one dose) (14%) 
• had travelled overseas – especially to countries experiencing measles cases. 

The findings of this report highlight that checking measles vaccination status is vital before travel. Clinicians are encouraged to check that all patients travelling overseas have had 2 doses of the measles vaccine at a minimum 4 weeks apart for full protection against measles. 

Unlike other travel vaccines, measles vaccine is free in NSW for people born during or after 1966 who have not had two doses of a measles containing vaccine, or with an uncertain measles vaccination history​, and infants 6 months to <12 months travelling to countries where measles is endemic, or where measles outbreaks are occurring. 

Education